The use of cylinder locks having a removable lock barrel is well known. Typically, in such locks the barrel is removably retained in the housing by a tumbler that is in the form of a control tumbler. When eccentrically displaced under the action of a spring, this control tumbler projects outwardly from the substantially cylindrical barrel (so that the control tumbler is extended relative to the barrel) and collaborates with a stop or a shoulder (wall) defined by a groove that is formed in the housing for preventing the removal of the barrel from the housing. In this fashion, the accidental removal of the lock barrel is prevented.
U.S. Pat. No. 2,061,456 issued to Falk discloses such a lock having a removable barrel with a control tumbler in which an extending end thereof is always extended relative to the barrel. The extending end has a pair of opposite rounded shoulders, so that the width of the extending end is reduced relative to the remainder of the control tumbler. When in the locking position, the extending end abuts a wall or shoulder that is formed in the barrel. In an unlocking position, the extending end coacts with slanted edges of a longitudinal slot, permitting removal of the barrel. In this fashion, the barrel can only be removed from the housing when the barrel is in the unlocked position, thereby preventing the accidental removal of the barrel when it is in the locked position.
U.S. Pat. No. 4,398,405 issued to Patriquin, provides a lock having a removable barrel equipped with a control tumbler that has a first end and a second opposite end. In one position, the first end is extended and the second end is retracted relative to the barrel, so that the barrel is retained in the barrel housing. In another position, the first end is retracted and the second end is extended relative to the barrel, so that the barrel may be removed from the housing. The first end of the control tumbler has a width that is greater than the width of the second end. Normally, the control tumbler is in the one position. Only when an appropiate key is inserted, is the control tumbler driven into the second position wherein the lock barrel may be removed. The barrel housing has at least one longitudinal slot formed therethrough. If a second longitudinal slot is provided, it terminates short of the end of the housing. When the first end is retracted and the extended second end is aligned with the longitudinal slot, the barrel may be removed from the housing.
While each of the above disclosures is useful for its intended purposes, they also have several disadvantages.
First, the barrels of such locks include a pair of opposite matched longitudinal slots that are intended to receive therein the various portions of the combinating tumblers of the barrel. In order to prevent the accidental removal of the lock barrel, at least one of the pair of matched longitudinal slots must terminate short of the annular groove while the other slot of the pair is in communication with the annular groove. Such an arrangement requires specialized tooling of the housing and/or the placement of specialized stops and inserts in the housing. This creates significant problems in manufacturing standardization and requires an increase in parts and inventories.
A second disadvantage regards the use of the control tumblers as the sole means for retaining the barrels in the housings thereof. In such locks, forced removal of the barrels from these locks places pressure on the control tumblers. Because these tumblers are often fabricated from steel and brass, while the barrels and housings are fabricated from a die cast zinc alloy, these tumblers are readily subject to deformation resulting from purposeful or accidental acts, such as overpushing of the key, overpulling of the barrel, etc.
Additionally, in the event that the system is of the type (such as Patriquin '405) that utilizes a first common key for locking and unlocking functions and a second key for removal functions, then anyone equipped even with only an appropiate second key (which is often a key that has simplified contours and, as such, is readily susceptible to being counterfeited) is able to dislodge and remove any of the barrels of the locks of the system, regardless whether the locks are locked or unlocked.
Finally, in an arrangement, such as that disclosed in Patriquin '405, in order to provide the appropiate annular groove, an arrangement is disclosed wherein the groove is open to the environment. Such a feature is not adaptable for use in locks having exterior applications, where it is exposed to the elements, such as snow, rain, etc., that can enter the internal workings thereof via the groove, thereby damaging the working of the lock. Also, the arrangements of Patriquin '405 require that different types of control tumblers and longitudinal slots be utilized depending on whether the barrel of the lock is to be rotatable 90.degree., 180.degree., 360.degree., etc. This creates further problems not only with manufacturing standardization, but also requires that a considerable inventory of parts, for the various tumblers, etc., of the locks be maintained.
Thus, it can be seen that there remains a need for a lock having a lock barrel which is removable therefrom only when in the unlocked position, which is capable of being fabricated so that it does not present problems with manufacturing standardization and maintainance of parts inventory, and which does not rely solely on the use of a control tumbler to retain the lock barrel in the housing, so as to be capable of withstanding greater amounts of stress than those of the prior art.